In the past, a lot of literatures have been introduced about a catalyst for producing ethylene oxide by vapor-phase oxidation of ethylene with molecular oxygen-containing gas, and a carrier thereof. For example, JP-A-55-145,677 discloses a production method of ethylene oxide consists of using a silver catalyst, in which silver and, if needed, further alkali metal component or alkaline earth metal component are supported on a nonacidic carrier, wherein total content of alumina, silica and titania is 99% by weight or more, and the metal content of each group of Va, VIa, VIII, Ib and IIb of the periodic table is less than 0.1% by weight as total amount of a metal oxides, and which does not show an acid color by the methyl red as indicator of pKa +4.8. In addition, there is proposed a catalyst for producing ethylene oxide (U.S. Pat. Nos. 5,077,256 and 5,395,812), in which silver and cesium are supported as catalyst components onto an α-alumina carrier wherein covering layer of amorphous silica is provided on the surface of the carrier.